JPH0770228A - Production of water absorbing resin - Google Patents

Abstract

PURPOSE:To obtain the subject resin excellent in water absorption rate and gel strength and useful for sanitary goods, etc., by adding untreated water- absorbing resin powder during drying after adding a treating liquid containing water, a dispersing agent and a crosslinkinga gent or immediately after finishing drying in treating the water-absorbing resin powder with the treating liquid. CONSTITUTION:In treating (B) a water-absorbing resin powder with (A) a treating liquid consisting of water, a dispersing agent and a crosslinking agent, during drying after adding the treating liquid A or immediately after finishing drying,(C) untreated water-absorbing resin powder is added thereto to provide the objective resin. Furthermore, when the objective resin is obtained, the water- absorbing resin used is a polyacrylic acid (co)polymer, etc., and the particle diameter has 5-400 mesh based on Tyler standard sieve. In the treating liquid A, amounts of components used based on 100 pts.wt. of the waterabsorbing resin are as follows. The crosslinking agent: 0.005-5 pts.wt.; the dispersing agent: 0.05-10 pts.wt.; water: 1-50 pts.wt.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a water absorbent resin.

[0002]

2. Description of the Related Art Since water-absorbent resins have a high water absorption capacity and excellent water retention ability, they are widely used not only in hygiene products such as diapers and sanitary products but also in fields such as agriculture, gardening, food and medicine. Has been done. Generally, a water absorbent resin is required to have high gel strength in addition to high water absorption and water retention. When the gel strength of the water-absorbent resin is weak, for example, in the case of diaper products, the water-containing gel becomes pasty, and the baby may lose its shape due to the weight and movement of the baby, which may cause diaper leakage. Further, when the gel strength is weak, the water-containing gel becomes large in stickiness, the wet back is deteriorated, and the quality of the diaper is deteriorated.

Therefore, conventionally, as a secondary treatment, the surface of the water-absorbent resin powder is treated to increase the gel strength. That is, JP-A-58-426
No. 02 publication discloses that a hydrophilic crosslinked polymer having a hydroxyl group or a carboxyl group is dispersed in a dispersion medium such as methanol or ethanol, and the surface is crosslinked with a crosslinking agent such as a polyvalent metal salt to obtain a water absorption rate and gel strength. Is disclosed.

[0004]

However, the secondary treatment as described above requires a stirring and mixing step and a drying step, and thus has a limited processing capacity. Therefore, it is difficult to perform the secondary treatment on all the water-absorbent resins in terms of treatment capacity. Therefore, it has been proposed to mix the untreated water-absorbent resin powder (primary treatment product) with the secondary-treated water-absorbent resin powder (secondary treatment product). Since the strength and other qualities are extremely inferior to those of the secondary treated product, they could not be put to practical use.

A main object of the present invention is to provide a method for producing a water-absorbent resin which has a quality capable of reducing the burden of secondary treatment and being practically used.

[0006]

Means and Actions for Solving the Problems In order to solve the above technical problems, the inventors of the present invention have conducted extensive studies, and as a result, untreated water-absorbent resin powder (primary treatment product) and secondary treatment The above-mentioned water-absorbent resin powder (secondary treated product) is not simply mixed, but the untreated water-absorbent resin powder is added and stirred and mixed during the drying after the treatment liquid addition in the secondary treatment step or immediately after the drying. At this time, new knowledge that a water-absorbent resin having a high quality that can be actually used can be obtained, and the present invention has been completed.

That is, in the method for producing a water-absorbent resin of the present invention, when the water-absorbent resin powder is treated with a treatment liquid consisting of water, a dispersant and a cross-linking agent, during the drying after the treatment liquid is added or immediately after the drying is finished. In addition, untreated water-absorbent resin powder is added. According to the present invention, since the untreated water-absorbent resin powder, which is the primary treated product, is mixed with the secondary-treated water-absorbent resin powder, the secondary treatment amount of the water-absorbent resin powder can be reduced, and the burden of the secondary treatment can be reduced. Is reduced. In addition, the obtained water-absorbent resin has a quality such as gel strength which is equal to or almost the same as that of the secondary treated product, and thus can be sufficiently practically used.

As the water absorbent resin used in the present invention, various conventionally used water absorbent resins such as crosslinked polyethylene oxide, crosslinked polyvinyl alcohol, crosslinked polyacrylic acid and its salts, and cellulose-
Examples thereof include acrylic acid graft copolymers and salts thereof, and hydrolysates of starch-acrylonitrile graft copolymers. Particularly, polymers having a carboxyl group and / or a carboxylate moiety, such as acrylic acid or acrylate in the main chain. It is preferable to use a polyacrylic acid-based water-absorbent resin composed of a polymer or copolymer having the monomer unit (1).

Examples of such polyacrylic acid-based polymers include polyacrylic acid, polyacrylic acid salts, and copolymers of acrylic acid and acrylic acid salts. Here, examples of the polyacrylic acid salt and the salt portion of the acrylic acid salt include alkali metal salts such as sodium salt and potassium salt, and organic base salts such as ammonium salt. Further, in order to improve properties such as hydrophilicity, it is a copolymer of a polymer having a monomer unit of acrylic acid or acrylate in its main chain and acrylamide, N-vinylpyrrolidone, 2-hydroxyethyl methacrylate or the like. May be.

The water-absorbent resin is preferably cross-linked, and known cross-linking means can be used for cross-linking. For example, by heating a copolymer with a cross-linking monomer such as N-methylol acrylamide, by using an oxidizing catalyst such as potassium peroxosulfate, or by using N, N having two or more polymerizable unsaturated bonds. It is possible to crosslink by adding a crosslinking agent such as'-methylenebisacrylamide, ethylene glycol diacrylate during the polymerization.

Usually, a method is adopted in which, if necessary, another copolymerizable monomer and the above-mentioned crosslinking agent are added to an aqueous solution of acrylic acid or an acrylic acid salt to carry out polymerization.
Since the polymer obtained by this method solidifies into a lump when dried, it is pulverized using a pulverizer into a particle size of a size suitable for a super absorbent polymer material. Since the polymer obtained by emulsion polymerization or suspension polymerization has a small spherical shape, it may be used as it is, or may be further pulverized into fine particles before use.

The water-absorbent resin powder (primary treated product) thus obtained preferably has a particle size of 5 to 400 mesh, preferably 16 to 150 mesh (110) on a Tyler standard sieve.
˜1000 μm) is more preferable. The treatment liquid for carrying out the secondary treatment of the water absorbent resin powder comprises water, a dispersant and a crosslinking agent.

The dispersion is used to prevent the generation of lumps due to aggregation during the secondary treatment and to carry out a uniform crosslinking treatment. Such dispersions include, for example, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, tripropylene glycol methyl ether. An ether compound such as tetraethylene glycol dimethyl ether; butanediol (eg, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol), pentanediol (eg, 1,5) -Pentanediol, 1,3-pentanediol, 2,3-pentanediol), hexanediol Such as 1,6-hexanediol, 2,5-hexanediol), 2-methyl -
Examples thereof include dihydric alcohols having 4 to 6 carbon atoms such as 2,4-pentanediol and 2-methyl-2,3-butanediol. The amount of the dispersant used is preferably 0.05 to 10 parts by weight with respect to 100 parts by weight of the water absorbent resin.
Further, it is preferably 2 to 50 parts by weight with respect to 100 parts by weight of water.

Water is added in order to make the cross-linking depth in the secondary treatment, that is, the depth from the surface of the cross-linked portion of the water absorbent resin uniform. The amount of water added is preferably 1 to 50 parts by weight with respect to 100 parts by weight of the water absorbent resin. The cross-linking agent added together with these water and dispersant has two or more functional groups capable of reacting with the water-absorbent resin. Such a cross-linking agent may be one that can react particularly with a carboxyl group or a carboxylate moiety of the water absorbent resin, and examples thereof include aldehyde compounds (glutaraldehyde, glyoxal, etc.), isocyanate compounds (for example, 2,4-tolylene diisocyanate). , Hexamethylene diisocyanate, etc., haloepoxy compound (eg epichlorohydrin, epibromohydrin etc.), epoxy compound (eg ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, dipropylene glycol) Diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, Li glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether), and the like polyvalent metal compounds. Among these crosslinking agents, an epoxy compound and an aluminum hydroxide gel obtained by the reaction of an aluminum salt with an aluminate or an aluminum salt with an alkali metal hydroxide (see JP-A-62-25072) are used. Is preferred.

The amount of these cross-linking agents added can be appropriately determined according to the desired water absorption characteristics, gel strength and the like.
Usually, 0.001 to 1 per 100 parts by weight of the water absorbent resin
It is used in an amount of 0 part by weight, preferably 0.005 to 5 parts by weight. Examples of the secondary treatment method include various methods. Generally, a water-absorbent resin powder is stored in a mixer,
A method in which a treatment liquid in which a dispersant and a cross-linking agent are dissolved or dispersed in water is dropped or sprayed with stirring, sufficiently mixed to perform cross-linking treatment, and then dried with a drier is used.

The mixer to be used is not particularly limited, and any mixer such as a Nauter mixer, ribbon blender, conical blender, Henschel mixer, and Raikai mixer can be used. Also, for the drying performed after the treatment, any ordinary dryer such as a hot air circulating dryer or a vacuum dryer can be used. Drying temperature is room temperature to 1
It is preferably 50 ° C., preferably 90 to 140 ° C., and the drying time is preferably set so that the water content is 1 to 7%.

In the present invention, the untreated water-absorbent resin powder is added and stirred and mixed during the drying after the addition of the treatment liquid or immediately after the completion of the drying. However, the addition of the untreated water-absorbent resin powder during drying requires time for cooling after the completion of drying, so it is preferable to add the untreated water-absorbent resin powder immediately after the completion of drying. Here, the term “immediately after completion of drying” refers to the time until the temperature of the product taken out from the dryer hardly decreases, specifically, the time until the temperature of the product does not decrease by 5 ° C. or more.

The stirring with the untreated water-absorbent resin powder may be performed in an open state, but it is preferable to perform the stirring in a closed state because the quality of the water-absorbent resin obtained by mixing the untreated water-absorbent resin is improved. . The reason for this is not clear, but it is considered that this is because the vapor of the treatment liquid is absorbed by the untreated water-absorbent resin to exert the secondary treatment effect. In order to stir and mix in a closed state, for example, the treated product may be put in a super mixer, covered and heated to stir and mix.

Even if the cooled secondary treated product after the treatment is heated and the untreated water-absorbent resin is mixed therein, the obtained product is inferior in quality and requires heating. It is not preferable. On the other hand, the quality is not sufficient even if the untreated water-absorbent resin is added in advance to carry out the secondary treatment. The amount of the untreated water-absorbent resin powder added during or immediately after the drying is 10 to 500 parts by weight, preferably 50 to 150 parts by weight, based on 100 parts by weight of the secondary treated water-absorbent resin powder. When the amount of the untreated water-absorbent resin powder added is less than 10 parts by weight, it is substantially the same as the secondary treated product, and the burden of the secondary treatment cannot be reduced. On the other hand, when the amount of untreated water-absorbent resin powder added exceeds 500 parts by weight, the quality such as gel strength becomes poor.

When the amount of untreated water-absorbent resin powder added is increased while the amount of treated liquid added is kept constant, the gel strength decreases. It is preferable to increase the amount of the liquid added accordingly. The secondary treated water-absorbent resin powder and the untreated water-absorbent resin powder are mixed by stirring for 2 to 5 minutes by using the above-mentioned mixer as they are, when the addition of the untreated water-absorbent resin powder is immediately after the completion of drying. Just go. In addition, when drying is in progress, stirring and mixing after drying are not particularly necessary, but it is preferable to perform a mixing treatment for uniform mixing.

[0021]

【Example】

Reference Example (Preparation of untreated water absorbent resin powder) 80% acrylic acid aqueous solution 75.0 parts by weight, 48.6% sodium hydroxide aqueous solution 54.9 parts by weight, deionized water 5
6.1 parts by weight were mixed to prepare an aqueous monomer solution having a neutralization degree of 80%.

Next, 1023 g of the obtained monomer aqueous solution
1% N, N'-methylenebisacrylamide aqueous solution
After adding 5 g, the dissolved oxygen was replaced with nitrogen gas.
Then, 33% of 1% potassium persulfate, 40 g of 1% potassium pyrosulfite and 0.04% aqueous solution of glyoxal 2
5 g were sequentially added and mixed over 15 seconds. The 0.04% aqueous solution of glyoxal was obtained by diluting glyoxal (40% aqueous solution, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) 100 times with water.

The obtained mixed solution was poured into a box-shaped container (15 cm in length, 20 cm in width, 4 cm in height) (made of SUS, inner surface treated with tetrafluoroethylene resin), and polymerization was carried out using a water bath at a temperature of 35 ° C. A hydrogel was obtained. This hydrogel is dried with a drum dryer to form flakes, which are pulverized with a pin mill to obtain a water-absorbent resin powder (primary treated product) having an average particle size of 42 mesh, which is composed of a cross-linked acrylic acid-acrylate copolymer. Obtained. Examples 1 to 7 (1) Preparation of treatment liquid for secondary treatment 1 g of diethylene glycol monoethyl ether as a dispersant and 0.1 g of ethylene glycol diglycidyl ether as a crosslinking agent were dissolved in 10 g of water to obtain a treatment liquid. (2) Secondary treatment Put 100 g of the primary treated product obtained in the reference example in a small stirrer,
While stirring, the whole amount of the treatment liquid was sprayed and added, and after stirring for another 2 minutes, the water content was adjusted to about 7%.
It was dried at a temperature of 0 ° C. The resin immediately after drying was placed in a small stirrer while still hot, and the above-mentioned primary treated products were further added in the amounts shown in Table 1, and the mixture was stirred and mixed for 3 minutes in either an open state or a closed state. The gel strength of the water-absorbent resin thus obtained in each example was measured. The results are also shown in Table 1. (Method of measuring gel strength) 0.9 in a 100 ml beaker
% Saline 60 g was added, and 2 g of the water-absorbent resin was added while stirring with a magnetic stirrer to cause gelation. After allowing the generated gel to stand for 8 hours, the hardness of the gel was measured using a card meter (manufactured by Iio Denki Co., Ltd.).

[0024]

[Table 1]

It can be seen from Table 1 that the water-absorbent resins obtained in the respective examples have high gel strength, although the gel strength decreases as the blending amount of the primary treated product increases. Further, from the comparison between Examples 3 and 7, a higher gel strength is obtained by stirring and mixing in the closed state than in the open state. Comparative Examples 1 to 6 The primary treated products obtained in Reference Examples were treated in the same manner as in Examples 1 to 7, dried and then left to cool without adding the primary treated products to obtain secondary treated products. Then, the secondary treated product 10 that has been sufficiently cooled.
0 g and the amount of the primary treated product shown in Table 2 were placed in a small stirrer and mixed with stirring for 3 minutes. With respect to the water absorbent resin of each comparative example thus obtained, the gel strength was measured in the same manner as described above. The results are also shown in Table 2. The resin temperature of the secondary treated product was 26 ° C.

[0026]

[Table 2]

From Table 2, as in Comparative Examples 2 to 5, Comparative Example 6 is obtained by simply mixing the primary treated product and the secondary treated product.
It can be seen that the gel strength is improved as compared with the case of the primary treatment product alone, but the gel strength is significantly reduced as compared with the case of the secondary treatment product of Comparative Example 1 alone. Examples 8 to 9 and Comparative Examples 7 to 9 The primary treated products obtained in Reference Examples were treated in the amounts shown in Table 3 and with the treatment liquids shown in the same table as in Examples 1 to 7, and shown in the same table. The primary treated product was mixed by stirring. With respect to the water absorbent resins of the respective Examples and Comparative Examples thus obtained, the gel strength was measured in the same manner as described above. The results are also shown in Table 3.

[0028]

[Table 3]

When the primary treatment products are mixed immediately after drying as in Examples 3, 8 and 9, the same amount of treatment liquid is used as in the comparative examples 7 to 9 in which the primary treatment products are mixed in advance. It can be seen that high gel strength can be obtained with. Further, although the amount of the primary treatment product added in Examples 8 and 9 was higher than that in Example 3, the gel strength was lowered by increasing the amount of the treatment liquid used than that in Example 3. Is prevented. Examples 10-12 and Comparative Examples 10-11 2 kg of the primary treated product obtained in Reference Example was placed in a small stirrer with a jacket (capacity: 10 liters), and the treated liquid (200 g of water, 20 g of diethylene glycol monoethyl ether and ethylene) was stirred. 2 g of glycol diglycidyl ether was mixed and dissolved) was added by spraying, and the mixture was further stirred for 3 minutes. Then, put steam into the jacket of the stirrer so that the water content becomes about 7%,
It was dried at 00 ° C. It took 25 minutes to dry. During these steps, 2 kg of the primary treated product was added at each stage shown in Table 4. After the completion of drying, stirring was continued for 5 minutes in order to keep the conditions of each sample constant. During that time, the introduction of steam into the jacket was stopped, and water was passed for 1 minute to cool it slightly. With respect to the water absorbent resins of the respective Examples and Comparative Examples thus obtained, the gel strength was measured in the same manner as described above. The results are also shown in Table 4.

[0030]

[Table 4]

From Table 4, it can be seen that the gel strength is highest immediately after the completion of drying when the primary treatment product is added, and then 20 minutes and 10 minutes after the start of drying. Comparative Example 12 100 g of the secondary treated product prepared in Comparative Example 1 was heated to a resin temperature of 95 ° C., put in a small stirrer, 100 g of the primary treated product was further added, and the mixture was sealed and mixed with stirring for 5 minutes. The gel strength of the obtained water absorbent resin was measured in the same manner as above, and it was 23000 dyn / cm ² .

[0032]

According to the present invention, since the untreated water-absorbent resin powder is mixed with the water-absorbent resin powder treated with the treatment liquid, the treatment amount of the water-absorbent resin powder can be reduced and therefore the treatment load is reduced. , Productivity is improved. In addition, by adding untreated water-absorbent resin powder during or immediately after drying after the treatment liquid is added, the resulting water-absorbent resin has an effect that it has a quality that can be sufficiently used in practice. .

Claims (1)

[Claims] 1. A method for producing a water-absorbent resin, which comprises treating a water-absorbent resin powder with a treatment liquid comprising water, a dispersant and a cross-linking agent, wherein untreated water absorption is carried out during or after the drying after the treatment liquid is added. A method for producing a water absorbent resin, which comprises adding a water-soluble resin powder.